Re: Confusing issue with redisplay

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Date: Thu, 19 Aug 2021 15:36:02 +0800
> 
> 
> I've run across an odd issue whilst bringing up a new window system: it
> seems that each glyph overlaps its surroundings by exactly one pixel,
> which leads to visible artifacting.  For instance, while I would have
> expected the output from redisplay to be as follows:
> 
> ["f" CHAR_GLYPH x=0 width=15 y=0 height=15] ["o" x=16 width=15 y=0
> height = 15]
> 
> In this case "o" would actually start at 15 on the X axis, causing the
> glyph "f" to be partially overdrawn.  What is even more confusing is
> that the output of redisplay seems to exhibit the same overlap under
> other window systems, whilst no artifacting is visible.

If "f" starts at 0 and its width is 15, then its last pixel is at
x=14, and the following glyph can start at x=15 without any overlap.

Or maybe you didn't tell enough details to understand what goes on
there.